This invention relates to blood staining systems and more particularly to the stabilization of Romanowsky type stains. Romanowsky type stains, e.g., Wright's solution and Giemsa's solution, comprise a methanol solution of Methylene Blue and an eosin dye along with other allied dyes. Typical allied dyes include Azure A, Azure B and Azure C.
In order to employ such a stain it is usually necessary to prepare a solution of the dry stain in methyl alcohol and apply the solution to a blood smear or the like. Next a buffer solution and a rinse solution are added stepwise to the stained smear until a visable physical change occurs.
The presence of a second dye in addition to Methylene Blue, particularly Eosin Y, is desirable to enhance the staining qualities of the solution. Other allied dyes, i.e., Azure A, Azure B and Azure C are also desirable for their enhancement of the solution's ability to stain the blood smear. The standard way of using the dye is to form the solution and allow it to stand for a period of time. The azure dyes in the stain powder are not very soluble in methanol. However, Methylene Blue degrades into azures in the presence of eosin upon aging in solution. It will normally take about two weeks of standing for optimal staining results to be achieved. Unfortunately, the dyes continue to oxidize, and the resultant oxidation products render the solution unsuitable for the intended purpose. Furthermore, random precipitation in the stain solution upon aging results in poor stain quality. Thus, while the stain solution takes about two weeks to become fully effective, it has a shelf life of only about 3 to approximately 12 months.
Gilliland et al disclose the use of HCl to stabilize a Romanowsky stain in Stain Technology, Vol. 54, No. 3, Pp. 141-150. The use of an acidic stain would, of course, be unsatisfactory in certain automated staining devices.
It is an object of the present invention to provide a non-acidic method for the stabilization of the above-described Romanowsky staining solutions.
It is a further object to provide a stabilized Romanowsky stain solution having a significantly increased shelf life.